1. Field of the Invention
The present invention relates to a thermoplastic elastomer powder composition for powder molding, a powder molding method using the same, and a molded article thereof.
2. Description of the Related Art
A powder molded article of a polyvinyl chloride powder composition containing a plasticizer is used for interior decorative materials of automobiles, for example, as a covering material for an instrument panel, a console box, an arm rest, a head rest and a door rim.
The molded article, however, has drawbacks in that the polyvinyl chloride has a poor lightweight property and poor non-pollution properties, because acidic substances generated by the thermal disposal of a motor vehicle cassation induce air pollution and acid rain, etc., and further, has drawbacks in that the plasticizer causes a clouding of the internal surface of a front window of automobiles. These drawbacks render the use of the above-mentioned molded article unsatisfactory.
The present inventors have studied ways in which to alleviate the drawbacks of the above-mentioned polyvinyl chloride powder composition, and previously proposed an olefin type thermoplastic elastomer powder for powder molding (see Japanese Patent Application Nos. 3-199579 and 3-199589).
Thereafter, the present inventors continued their studies, and as a result, encountered a problem that, although the thermoplastic elastomer powder exhibits a good flowability immediately after the preparation by pulverization, an aggregation occurs among the powder particles when the powder is allowed to stand for a long time, and thus the powder no longer exhibits the flowability necessary for powder molding.
Further, when use is made of a powder slush molding method, which comprises bringing a powder into contact with a heated mold to heat-fuse powder particles to each other and returning powder particles not subjected to heat fusing to a powder feed box, the repeated use of the powder not subjected to heat fusing causes the powder to be gradually heated, and this heat is stored in the powder feed box. This gradually causes an aggregation between powder particles to occur, which deteriorates the flowability of the powder, so that a continuous operation for a long time gives rise to the production of molded articles having an underfill and pin holes.